The prinicipal objective of the proposed research is to delineate the manner in which microsomal UDP-glucuronyltransferase reactions are regulated. This objective will be pursued along 3 separate but interrelated lines of work. (1) Efforts will be extended and expanded on the purification of glucuronyltransferases with different aglycone specificities. The role of these studies in the overall program is to provide suitable preparations of enzymes for (a) studies of the relationship between structure and function in different forms of glucuronyltransferase; (b) mapping of active sites on the inside/outside of the vesicular bilayer; and (c) detailed studies of lipid-protein interactions. (2) Work will continue on defining the properties of phospholipids essential for activating glucuronyltransferase, using partially purified, phospholipid-free preparations. It is known already that interactions between glucuronyltransferase and its lipid environment are important determinants of the function of these enzymes. The objective of these studies is to understand the chemical and physical properties of phospholipids that are important for modifying the kinetic properties of glucuronyltransferase. (3) We will study the effects of phospholipids on the properties of several glucuronidation reactions. The proposed work also includes studies of glucuronidation reaction in intact microsomes in order to define the regulatory parameters for each type of reaction. These latter studies will provide baseline data for interpreting results from reconstitution experiments.